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Inversion between verts and inverts (was CREB?)

Richard Norman rsnorman at mw.mediaone.net
Fri Apr 16 21:19:21 EST 1999


The discussion in Zigmond et al (cited below) does not mention
whether the relationship between Urbilateria and flatworms.  I
would also worry about nematodes who have both a dorsal and
a ventral nerve cord.

I haven't yet read the citations, but I disagree that Saint Hillaire
had any grain of correctness in the inversion hypothesis.  True,
there is a mechanism directing dorsal-ventral differentiation and
that might be shared among all metazoa, as are many genetic
systems for controlling how to build a complex multicellular body.

But you don't get a vertebrate nervous system by turning an embryo
upside down or by building an arthropod one on the wrong side
of the body!  The whole neural tube idea is novel.

I think it is more like:  OK, we both know top from bottom the same
way.  Now where do I put things?  You really put your nervous system
on
the bottom, below the digestive system and heart?  How weird, I did
it the other way around!  It takes all kinds!



hemidactylus at my-dejanews.com wrote in message
<7f821a$brc$1 at nnrp1.dejanews.com>...
>In article <3714FFB8.4F0C4294 at umich.edu>,
>  Richard Norman <rnorman at umich.edu> wrote:
>> I don't remember what this thread was originally called,
>> it has scrolled off my news group, but I have found
>> some new info.
>>
>It was called "CREB?". It was I who spawned it. Thank you for
looking.
>>
>> "Fundamental Neuroscience" (Zigmond, Bloom, Landis, Roberts
>> and Squire, Academic Press, 1999) refers to this notion in
>> Box 2.5 on page 19, "How to turn a lobster into a vertebrate".
>>
>> It attributes the notion of inversion of the dorsoventral axis
>> to E Geoffroy Saint-Hilaire in 1822.  It also cites recent
>> studies on the patterning of the dorsoventral axis in the
>> "Urbilateria", a precursor and common ancestor of arthropods
>> and chordates:
>>
>Was this discussed as a "flatworm ancestor"?
>>
>>     DeRobertis, E.M. and Y. Sasai, A common plan for dorsoventral
>>     patterning in Bilateria. Nature 380:37-40(1996)
>>
>>     Hogan, B.L.M. Upside-down ideas vindicated.  Nature 376:210-211
>>     (1996).
>>
>
>Thank you for the references, Richard. Geoffroy wasn't so far off the
mark, I
>guess. Too bad those scientists way back when couldn't enjoy the
molecular
>techniques used today. Of course 100-200 years from now, people might
be
>saying similar things about the scientific greats of our time.
>
>--
>Scott Chase
>
>
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